The invention relates to a stitch control method of operation an electronic sewing machine having an electronic memory storing stitch control data which are sequentially read out to control the stitch forming device of the sewing machine to produce various stitches of patterns.
Generally in electronic sewing machines, the fabric feed control motor controls the feed regulator at a rotation phase of the sewing machine when the needle penetrating a sewn fabric is coming up out of the needle plate, and the needle position control motor controls the needle at another rotation phase of the sewing machine when the needle is high up above the needle plate.
The invention has been provided to considerably reduce the totoal output of the needle position and fabric feed control motors which sequentially control the needle position and the fabric feeding movement, to thereby disperse the output density of the two control motors, to thereby moderate the control time period allotted to each of the control motors, and thereby to reduce the size as well as the capacity of the control motors.
According to the prior art, the control of the needle position is made, as shown in FIG. 1, in the rotation phase (a-b) of the sewing machine which phase is higher than the level H.sub.1 above the needle plate 3 and is depicted by the moving locus 2 of the needle point 1 in relation to the rotation angle of the drive shaft of the sewing machine which is to be considered in the lateral direction. On the other hand, the control of the fabric feeding movement is made in the rotation phase (c-d) of the sewing machine, which phase is lower than the level H.sub.2 below the needle plate 3 and is depicted by the moving locus 4 of the feed dog (not shown). Due to the function and structure of the sewing machine, there is, as shown, a control prohibition phase (b-c) between the phase (b) at which the control of the needle is to have been finished and the phase (c) at which the control of the feed dog is starting. On the other hand, there may be a phase (a'-d) in which the two control motors are required to be controlled at the same time in dependence upon the sizes of stitches. In such a case, it is required to provide so much capacity of power source and control motors, and also the control becomes so complex. Actually it has been designed to avoid the simultaneous actuation of the two control motors in such a phase (a'-d).
In this connection, it becomes necessary to explain the formation of stitch patterns as shown in FIGS. 2A and 2B in reference to FIGS. 6 and 7 showing the stitch control data of the respective patterns. The needle control data 0 corresponds to the needle position R at the right side end of the maximum needle swinging amplitude, and the data 30 corresponds to the needle position L at the left side end of the maximum needle swinging amplitude. The feed control data 0 corresponds to the muximum feeding amount (about 2.5 mm) in the back direction. The feed control data 15 corresponds to no feeding amount, and the data 30 corresponds to the maximum feeding amount (about 2.5 mm) in the forward direction. Further, it may be a feed control data 45 (though not shown) which corresponds to the maximum feeding amount (about 5 mm) in the forward direction by manual adjustment. The control amounts in FIGS. 6 and 7 are the difference values between the data of the preceding stitches and the data of the following stithces.
The stitch control data in FIG. 6 are employed to sequentially produce the stitches 1-6 forming a unit of pattern in FIG. 2A with the following stitch (1) for another same unit of pattern. Similarly the stitch control data in FIG. 7 are employed to produce the stitches 1-2 forming a unit of pattern in FIG. 2B with the following stitch (1) for another unit of pattern. In FIGS. 6 and 7, the maximum feed and needle control amount is 30 implying that the feed and needle control motors are required to operate to the maximum extent for each stitch of the pattern. The maximum sum total of the feed control amount and the following needle control amount is 30 (45 in the manual adjustment) in FIGS. 6 and 7, which is considerably smaller than 60 (75 in manual adjustment). It is therefore apparent that all region of phase (c-d) may be used to control the feed control motor with control amount 30 and that the region of phase (d-b') is enough to finish the control of the needle control motor because the control amount is far below 30. If the feed control amount is below 30 and the needle control amount is 30, the feed control motor may be controlled in the phase (c-a') and the needle control motor may be controlled in the phase (a'-b'). It is therefore possible to determine the capacity of the control motors in accordance with the maximum output to be produced by the motors within a period of time defined by the phases (c-d) and (a'-b).
However it often happens during the actual stitching operation that the total control amount of the feed and needle control motors comes up to 60 when a new pattern is selected during a stitching operation of one pattern. FIG. 3 shows such an embodiment of the pattern. In reference to FIG. 1, if a new pattern is selected at a phase before a phase (a) or (a', a"), it is to be assumed that a new data is read out at the phase (a) or (a', a") for controlling the needle and feed dog. More precicely, if the pattern in FIG. 2B is selected, during the formation of the pattern in FIG. 2A, in the phase (a-a') corresponding to the phase before the phase (a) at which the stitch 4 is formed up, the feed control data in the phase (c-d) is 0 for forming the stitch 5 in FIG. 2A and the feeding amount is 0, and the needle control data is 30 for the stitch 4. Then at the phase (a') the needle control data 0 is read out for forming the stitch 1 in FIG. 7 corresponding to the stitch 1' in FIG. 3, and the feed control data 30 is going to be read out for forming the stitch 2. In the phase (a'-b'), the control amount of the needle is 0-30=30. Thus the total amount (the absolute value) is 30. However, in the following phase (c'-d') the feed control amount for the stitch 2 is 30-0=30 because the feed control data is 30, and at the phase (a") the needle control data 30 is read out for the switch 2 in FIG. 7 and the feed control data 30 is read out for the stitch (1). Therefore, in the phase (a"-b") the needle control amount is 30-0=30. Thus, the total control amount (the absolute value) is 60.
The feed and needle control motors have to be controlled each with the maximum control amount 30 in the phase (c'-b"), and have to be switched over in the phase (a"-d'). In dependence upon the switchover point to be taken within the phase (a"-d'), one of the control motors is so much loaded while the other is so less loaded. Provided that the switchover of the control motors is made at the intermediate point (e) of the phase (a"-d') for the convenience sake, the feed and needle control motors, which are designed to be normally controlled to the maximum amount in the phases (c'-d') and (a"-b"), respectively, for the repeating formation of the same pattern, would be short of capacity and may be led to erroneous operation due to the shortened control time of the motors defined by the phases (e-d') and (a"-e) respectively in case a new pattern is selected during the formation of the pattern. In order to avoid such undesirable effects, it becomes necessary to increase the size as well as the capacity of the control motors.